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Abstract:

A trigger assembly for a trigger housing for a, M249 fully automatic
rifle is provided having a switch accessible at the outside of the
trigger housing for changing the firing of the rifle between
semi-automatic and fully-automatic fire.

Claims:

1. A trigger assembly fitted to a trigger housing that is adapted to
engage a receiver for an M249 Assault Rifle, the receiver carrying an op
rod assembly that reciprocates within the receiver to fire the rifle, the
trigger assembly comprising: (a) a sear pivotally mounted to the trigger
housing, the sear providing: (i) a sear tip, and (ii) a latch end; (b) a
sear spring biasing said sear to pivot to position said sear tip in the
path of the op rod assembly when the trigger housing is engaged with the
receiver and the trigger assembly is unactuated; (c) a trigger pivotally
mounted to the trigger housing; (d) a disconnector pivotally connected to
said trigger, said disconnector providing: (i) a ramped surface, and (ii)
a catch end adapted to engage said latch end of said sear; (e) a select
fire mechanism including: (i) a switch accessible outside of the trigger
housing and selectively movable between a fully automatic firing position
and a semi automatic firing position, (ii) a selector body including a
fully-automatic selector surface and a semi-automatic selector surface,
said selector body positioned within the trigger housing and associated
with said switch such that moving said switch between said fully
automatic firing position and said semi-automatic firing position also
moves said selector body between a fully automatic firing position and a
semi-automatic firing position; and (f) a disconnector spring biasing
said disconnector toward said sear and said selector body, wherein
actuating the trigger assembly draws said ramped surface of said
disconnector against said selector body and, when said switch is in said
fully-automatic firing position, said ramped surface is drawn against
said fully-automatic selector surface and, when said lever is moved to
said semi-automatic firing position, said ramped surface is drawn against
said semi-automatic selector surface, and wherein, when said ramped
surface is drawn against said fully-automatic selector surface, said
catch end of said disconnector engages said latch end of said sear and
pulls thereon so as to pivot said sear tip out of the path of the op rod
assembly and remain out of said path until said trigger is released, and,
when said ramped surface is drawn against said semi-automatic selector
surface, said catch end of said disconnector engages said latch end of
said sear and pulls thereon so as to pivot said sear tip out of the path
of the op rod assembly and thereafter disengages such that said sear
pivots on said sear spring to again extend into the path of the op rod
assembly after a single firing of the M249 Assault Rifle.

2. The trigger assembly as in claim 1, wherein said switch is a lever
connected to said selector body.

3. The trigger assembly as in claim 2, wherein said selector body is a
longitudinal member that rotates about its longitudinal axis within the
housing as said lever is moved, said selector body including a clearance
cut, wherein said semi-automatic selector surface is a peripheral contact
surface of the longitudinal member and said fully-automatic selector
surface as an inset clearance cut surface in said longitudinal member.

Description:

FIELD OF THE INVENTION

[0001] This invention relates to an M249 machine gun including a select
fire mechanism that permits the gun to be selectively operated to be
either fully automatic or semi automatic.

BACKGROUND OF THE INVENTION

[0002] This invention provides a select fire mechanism for an M249
automatic rifle that permits the rifle to be operated to be either fully
automatic or semi-automatic. The trigger assembly of this invention
replaces what would be the typical trigger assembly of the M249, which
effects fully automatic fire. The replacement of the standard M249
trigger assembly with the trigger assembly of this invention permits the
rifle to be operated to be either fully automatic or semi-automatic
according a selection made by the shooter.

[0003] In the M249 fully automatic rifle, the sear, which is part of the
trigger assembly, holds back a spring-loaded operation rod assembly
(herein "op rod assembly"), which is retained in the receiver, and
pulling on the trigger pulls the sear out of engagement with the op rod
assembly, thus permitting the op rod assembly to move under the influence
of the spring acting upon the op rod assembly. Once released, the op rod
moves forward and cycles internal striking mechanisms that cause a
cartridge to be fired. Thereafter, expanding gases from the ignition of
powder in the cartridge furnish the energy for the continued fully
automatic operation or cycling of the rifle.

[0004] Immediately after firing, as the bullet traverses the barrel and
passes an internal gas port prior to exiting from the muzzle, the live
gases expand through appropriate ports to force the op rod assembly back
against the bias of the spring that forces the op rod assembly toward the
cartridge chamber. This loads the spring, and, once the pressure of the
expanding gases dissipates, the spring again forces the op rod assembly
forward to fire another round. So long as the trigger remains pulled, the
sear remains out of the path of the op rod assembly, and the rifle
continues to fire until the ammunition is exhausted. If the trigger is
released, the sear moves back into the path of the op rod assembly,
stopping the same and holding it in a spring-loaded position from which
it can fire another round upon a subsequent squeezing of the trigger.

[0005] Because fully automatic fire is not always needed and not always
desired, there is a need in the art for a rifle that includes a select
fire mechanism permitting the rifle to be selectively operated as a fully
automatic firearm or a semi automatic firearm.

SUMMARY OF THE INVENTION

[0006] The present invention generally provides a trigger assembly fitted
to a trigger housing that is adapted to engage a receiver for an M249
Assault Rifle. As known for the M249 Assault Rifle, the receiver carries
an op rod assembly that reciprocates within the receiver to fire the
rifle. The trigger assembly of this invention includes a sear pivotally
mounted to the trigger housing, the sear providing a sear tip and a latch
end. A sear spring of the trigger assembly biases the sear to pivot to
position the sear tip in the path of the op rod assembly when the trigger
housing is engaged with the receiver and the trigger assembly is
unactuated. The trigger assembly further includes a trigger pivotally
mounted to the trigger housing, and a disconnector pivotally connected to
the trigger. The disconnector provides a ramped surface and a catch end
that is adapted to engage the latch end of the sear. The trigger assembly
further includes a select fire mechanism including a switch that is
accessible outside of the trigger housing and selectively movable between
a fully automatic firing position and a semi automatic firing position,
and a selector body is associated with the switch. The selector body
includes a fully-automatic selector surface and a semi-automatic selector
surface, and moving the switch between the fully automatic firing
position and the semi-automatic firing position also moves the selector
body between a fully automatic firing position and a semi-automatic
firing position. A disconnector spring biases the disconnector toward the
sear and the selector body, and actuating the trigger assembly draws the
ramped surface of the disconnector against the selector body and, when
the switch is in the fully-automatic firing position, the ramped surface
is drawn against the fully-automatic selector surface and, when the lever
is moved to the semi-automatic firing position, the ramped surface is
drawn against the semi-automatic selector surface. When the ramped
surface is drawn against the fully-automatic selector surface, the catch
end of the disconnector engages the latch end of the sear and pulls
thereon so as to pivot the sear tip out of the path of the op rod
assembly and remain out of the path until the trigger is released, and,
when the ramped surface is drawn against the semi-automatic selector
surface, the catch end of the disconnector engages the latch end of the
sear and pulls thereon so as to pivot the sear tip out of the path of the
op rod assembly and thereafter disengages such that the sear pivots on
the sear spring to again extend into the path of the op rod assembly
after a single firing of the M249 Assault Rifle.

[0007] In a particular embodiment, the switch is a lever connected to the
selector body, and the selector body is a longitudinal member having a
longitudinal axis about which the longitudinal member rotates as the
lever is moved. In this particular embodiment, the selector body includes
a clearance cut defining a peripheral contact surface and a clearance cut
surface. The peripheral contact surface serves as the semi-automatic
selector surface in this embodiment, and the clearance cut surface serves
as the fully-automatic selector surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a side view of a select fire trigger assembly in
accordance with this invention, showing the external grip portion and a
lever that permits the selection of the type of firing;

[0009] FIG. 2 is a cross section taken through the center of the sear and
showing the internal components of the select fire trigger assembly in
accordance with this invention, the components being shown in semi-auto
mode, with the trigger at rest;

[0010] FIG. 2A is an enlarged view of the detail identified in FIG. 2 as
Detail 2A;

[0011] FIG. 3 is a cross section taken through the center of the sear and
showing the internal components of the select fire trigger assembly in
accordance with this invention, the components being shown in semi-auto
mode, with the trigger pulled to the position where the sear releases
from the disconnector;

[0012] FIG. 4 is a cross section taken through the center of the sear and
showing the internal components of the select fire trigger assembly in
accordance with this invention, the components being shown in full-auto
mode, with the trigger at rest;

[0013] FIG. 5 is a cross section taken through the center of the sear and
showing the internal components of the select fire trigger assembly in
accordance with this invention, the components being shown in full-auto
mode, with the trigger pulled and the sear remaining associated with the
disconnector.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0014] This invention relates to the M249 Automatic Rifle, Caliber
5.56×45 mm, including known model variations. Particularly it
relates to the conversion of an M249 to provide the same with a mechanism
to selectively cause the rifle to fire in either a fully automatic or
semi-automatic mode. This "conversion" may be in the form of replacing
the trigger assembly of an M249 with a trigger assembly in accordance
with this invention, or might be in the form of creating an M249 from
scratch having select fire capabilities.

[0015] In the present invention, a select fire trigger assembly provides
the desired select fire mechanism. Relevant portions of the select fire
trigger assembly are shown in FIGS. 1-5. The select fire trigger assembly
140 is provided in a trigger housing 141 that connects to an M249
receiver to communicate with the M249 striking mechanisms. The trigger
housing 141 connects to the receiver (known, not shown) so that the
trigger assembly 140 can communicate with an op rod assembly (known, not
shown) retained within the receiver. The trigger assembly 140 can be
manipulated to allow or prevent the reciprocation of the op rod assembly
and hence allow or prevent firing.

[0016] The select fire trigger assembly 140 includes a trigger 142 that is
pivotally carried on a trigger pin 144. The crescent portion of the
trigger 142 is below the pivot point established by the trigger pin 144,
but the body of the trigger 142 extends above that pivot point to
interact with a disconnector 146 pivotally secured to the trigger 142 by
a disconnector pin 148. The disconnector 146 is biased by a disconnector
spring 150 to engage a latch end 152 of a sear 154. The disconnector
spring 150 is a compression spring acting between a mount 143 on the
trigger 142 and a mount 147 on the disconnector 146 and applies force
between the two such that the disconnector 146 is forced against the sear
154 and/or a selector body 164. It should be noted that, in FIGS. 2-5,
the disconnector spring 150 is shown as being slightly off of the mount
147 merely as a result of the program employed to create the figures, and
it should be appreciated that the mount 147 provides the area of receipt
for the end of the disconnector spring 150 that is opposite the end
secured at the mount 143 on the trigger 142. The pulling of the trigger
142 (rightward in the drawings) causes the disconnector 146 to be pulled
forward and interact with the sear 154 and the selector body 164 as will
be described more fully below.

[0017] The sear 154 is itself biased for limited rotational movement by a
sear spring 156. The sear spring 156 is shown as a torsion spring, being
wound about a sear spring pin 155 and having one end extending to act
upon the sear 154 and another end extending to act upon a sear spring
stop pin 157. Though a torsion spring is a preferred spring due to the
force it can impart against the sear 154, other springs could be mounted
in the trigger housing 141 to function in a similar manner. The sear 154
provides a sear tip 158 that, at rest (FIG. 1), extends above the top
boundary of the trigger housing 141 so that, when the trigger housing 141
is connected to a receiver for an M249 Rifle, it can engage a sear ledge
provided on the op rod assembly, as generally known.

[0018] The select fire trigger assembly 140 includes a select fire
mechanism 160 that provides a lever 162 to be moved between a
semi-automatic firing position (shown at the work "semi" in FIG. 1,
though the "s" is covered by the lever 162) and a fully automatic firing
position (shown in phantom in FIG. 1, where the lever 162 points to
"full"). The lever 162 is accessible at the exterior of the trigger
housing 141 so that it can be moved between these positions. As their
names imply, when the lever 162 is moved to the semi-automatic firing
position, the trigger assembly 140 will function to permit a single
cycling of the op rod assembly, and hence semi-automatic firing, when the
trigger 142 is squeezed, and, when the lever 162 is moved to the
fully-automatic firing position, the trigger assembly 140 will function
to permit continuous cycling of the op rod assembly, and hence
fully-automatic firing, so long as the trigger 142 remains pulled.

[0019] With reference to FIGS. 2-5, the select fire mechanism 160 alters
the functioning of the trigger assembly 140 by means of a selector body
164, which is connected to the lever 162 so as to rotate when the lever
162 is pivoted between the semi- and fully-automatic firing positions.
The selector body 164 is positioned between the disconnector 146 and the
sear 154, and serves as a stop for both the disconnector 146, as its
ramped surface 166 is pushed against the selector body 164 by
disconnector spring 150, and the sear 154, as its front end 168 is forced
against the selector body 164, about sear pin 170, by the sear spring
156. The selector body 164 includes a clearance cut 172, which defines a
peripheral contact surface 174 and an inset contact surface 176 (see FIG.
2A), and it is this clearance cut 172 that is repositioned by movement of
the lever 162 to bring about the desire firing, semi or full automatic.

[0020] In FIGS. 2 and 3, the trigger assembly 140 is shown in the
semi-automatic firing position. In FIG. 2, the trigger 142 is at rest,
whereas, in FIG. 3, the trigger 142 has been pulled to the point where
the sear tip 158 is outside of the path 200 of the sear ledge of the op
rod assembly such that the sear tip 158 releases the op rod assembly for
reciprocation. The select fire mechanism 160 is thus in the
semi-automatic firing position. In this position, the ramped surface 166
of the disconnector 146 faces the selector body 164 with the selector
body 164 positioned between the front end 168 of the sear 154 and the
sloped surface. When the trigger 142 is pulled, as shown, the
disconnector 146 is pulled forwardly at disconnector pin 148 pulling the
ramped surface 166 of the disconnector 146 against the peripheral contact
surface 174 of the selector body 164, thus forcing the disconnector 146
to also move downwardly against the disconnector spring 150. Notably, the
clearance cut 172 is not engaged by the ramped surface 166, rather, the
ramped surface 166 engages the peripheral contact surface 174, thus
bringing about a larger downward movement than would be achieved if the
ramped surface 166 engaged the inset contact surface 176. The forward and
downward movement causes the catch end 178 of the disconnector 146 to
pull on the latch end 152 of the sear 154, thus causing the sear 154 to
pivot about the sear pin 170 until the sear tip 158 is made to disconnect
from the sear ledge of the op rod, thus leading to the firing of a
cartridge. The sear tip 158 pivots downwardly, out of the path 200 of the
op rod assembly and thus out of engagement with the sear ledge provided
on the op rod assembly. At substantially the same time, the disconnector
146 disconnects from the sear 154, as shown right at the point of sear
release, represented at 180 in FIG. 3.

[0021] After this disconnection, the sear 154 is able to move
independently of the trigger 142, under the influence of the sear spring
156, to again extend into the path 200 of the op rod assembly and catch
the sear ledge as it travels back under the influence of the expanding
gases from the firing of the cartridge. The selector body 164 provides a
stop for the pivoting of the sear 154 under the influence of the sear
spring 156, and the sear 154 returns to its rest position. At the rest
position, the sear 154 can be reengaged with the trigger 142, at the
disconnector 146, when the trigger 142 is released. Then the trigger 142
can be pulled again to fire another cartridge, and so on. Thus, in the
semi-automatic firing position, the selector body 164 is positioned to
cause a complete disengagement of the disconnector 146 from the sear 154,
permitting the sear spring 156 to return the sear 154 to a position to
engage the sear ledge of the op rod assembly and thus halt firing after
the firing of one cartridge.

[0022] In FIGS. 4 and 5, the trigger assembly 140 is shown in the
fully-automatic firing position. In FIG. 4, the trigger 142 is at rest,
whereas, in FIG. 5, the trigger 142 has been pulled to the point where
the sear tip 158 is outside of the path 200 of the sear ledge and op rod
assembly such that the sear tip 158 releases the op rod assembly for
reciprocation. The select fire mechanism 160 is thus in the
fully-automatic firing position. In this position, the ramped surface 166
of the disconnector 146 faces the selector body 164 with the selector
body 164 positioned between the front end 168 of the sear 154 and the
sloped surface. But in contradistinction to the positioning shown in the
semi-automatic firing position, the selector body 164 has been rotated by
movement of the lever 162 such that, when the trigger 142 is pulled, as
shown, the disconnector 146 is pulled forwardly at disconnector pin 148
pulling the ramped surface 166 of the disconnector 146 against the inset
contact surface 176, as opposed to the peripheral contact surface 174 of
the selector body 164. Thus though the disconnector 146 is moved
downwardly against the disconnector spring 150, similarly to the movement
experienced in the semi-automatic firing position, the downward movement
is smaller than would be achieved if the ramped surface 166 engaged the
peripheral contact surface 174. This engagement (or lack of
disengagement) is shown in FIG. 5 at numeral 182. As a result, the catch
end 178 of the disconnector 146 will pull on the latch end 152 of the
sear 154 but will not disengage from the latch end 152, as occurs in the
semi-automatic firing position. The sear 154 will pivot about the sear
pin 170 until the sear tip 158 is made to disconnect from the sear ledge
of the op rod, thus leading to the firing of a cartridge. The sear tip
158 pivots downwardly, out of the path 200 of the op rod assembly and
thus out of engagement with the sear ledge provided on the op rod
assembly, and, because the disconnector 146 does not disconnect from the
sear 154, the sear tip 158 will remain out of the path 200 of the sear
ledge so long as the trigger 142 remains pulled, and the op rod assembly
will continue to cycle and fire in a fully automatic mode. Releasing the
trigger 142 will permit the sear spring 156 to return the sear 154 to the
rest position where it is able to engage the sear ledge of an op rod
assembly and halt the firing until the trigger 142 is pulled again.

[0023] In accordance with this invention, a fully automatic M249 Assault
Rifles in which an op rod assembly reciprocates to effect fully automatic
fire during such time as a sear remains outside of the path 200 of a sear
ledge of the op rod assembly can be altered with the trigger assembly as
taught herein to be selectively made to operate in either fully automatic
or semi-automatic modes.